As mentioned above the present invention relates to safety razors with blades units arranged to be capable of pivoting movement relative to the handles, on which the blade units are carried, in the course of shaving. The pivoting motion allows the blade unit to follow more easily the skin contours so that the exact angle at which the handle is held relative to the skin is less critical to achieving a good shaving performance and efficiency. Razors with pivotal blade units have been successfully marketed for many years. The pivot axis, which usually extends parallel to the cutting edges of the blades, can be defined by a pivot structure by means of which the handle is connected to the blade unit. Alternatively the blade unit may include an attachment member to which a frame or housing incorporating the blade or blades and other skin contacting parts is pivotally connected. A blade unit of this form described in WO 97/37819, the content of which is incorporated herein by reference, has an attachment member in the general form of a yoke with a hub for engagement with the upper end of the handle and a pair of oppositely directed arms provided with pivot journals at their ends for engagement in sockets provided at the ends of the frame. Retention clips are applied around the respective ends of the frame to maintain the pivot journals within the sockets.
Various positions of the pivot axis relative to the blade edges have been proposed and used, including positions above and below a plane tangential to the guard and cap surfaces, and positions in front of, behind and in the region of the blade edges. There is generally a rest position to which the pivotable blade unit is biased by a spring arrangement and many different forms of mechanical spring arrangement have been suggested in the prior art.
The blade unit can be mounted to pivot in either direction from the rest position, but it has been found advantageous to have the pivot axis located in front of the blades, more exactly in the vicinity of the guard, below the plane tangential to the guard and cap surfaces, and for the blade unit to be arranged to pivot in one direction only from the rest position, as described in WO 93/10947. In the Mach 3 razor currently marketed by the Applicant, the blade unit is pivotally mounted in this manner. It includes an attachment member as described above for connection to the handle, and there is a spring-loaded plunger that projects from the handle and through the hub of the attachment member to bear on the underside of the frame to bias the blade unit to the rest position. A small coil spring urges the plunger outwardly. The frictional effects which are unavoidable with such a mechanical spring arrangement are difficult to control with the result that a smooth and consistent pivoting performance is difficult to guarantee.
The present invention addresses this drawback by employing a magnetically generated return force. Prior art proposals in which magnets are provided in safety razors include those described in: U.S. Pat. No. 2,885,778, wherein magnets are employed to hold a removable blade when the razor head is opened, e.g. for rinsing away shaving soap and debris; U.S. Pat. No. 3,740,841, wherein a blade is mounted on a pivotal carrier to be retractable against a bias, from a normal shaving position relative to a fixed guard, when excessive forces are exerted on the blade, and either a spring or a pair of magnets applies the bias; U.S. Pat. No. 5,526,568, wherein a blade unit is rotatable about an axis perpendicular to the length of the blade unit, and a mechanism incorporated in the handle for adjusting the blade unit position can include magnets for maintaining the blade unit in the adjusted position; U.S. Pat. No. 6,035,535 in which magnets are employed to attach a flexible shaving cartridge to a razor handle; FR 2660589, wherein a pivot structure connecting a razor head to a handle incorporates magnets to hold the razor head in the pivotal position to which it is adjusted; and RU 2093349, wherein a pivotal blade unit is urged to an initial working position by a permanent magnet disposed on the handle to attract the underside of the blade unit the arrangement being such that the attraction will diminish as the blade unit pivots away from the initial position.